It is known to heat liquid by rotating a rotor in a reservoir of liquid, such an arrangement being shown in the patent to Perkins U.S. Pat. No. 4,798,176 assigned to the same assignee as the present application. In that patent scoops at the periphery of a rotor pick-up liquid as the rotor is rotated and direct the liquid through inwardly directed passages in the rotor to a central outlet cavity in the rotor which is in open communication with a central outlet port in the rotor housing. This arrangement was found to deal satisfactorily with cavitation problems but the liquid driven inwardly was opposed by centrifugal force tending to drive the liquid outwardly. In other words, though the arrangement addressed cavitation problem, it clearly was not as efficient as it could have been.
Another arrangement for preventing cavitation while taking advantage of centrifugal force is shown in a patent to Perkins U.S. Pat. No. 4,779,575. That patent involves the use of pump means which delivers liquid to a central cavity in a rotor from which liquid is expelled by centrifugal force through passages in the rotor to its periphery whence the liquid flows through an outlet in the rotor housing to a heat utilization device. Because the pump operated on the scoop principal similar to the rotor in U.S. Pat. No. 4,798,176 the pumped liquid was again subject to opposing forces tending to reduce the overall efficiency of the heater.
The broad object of the present invention is to provide a heater for heating liquid by friction but with enhanced efficiency over prior systems.